Liquid aspirating method

ABSTRACT

The present invention aims to shorten an aspiration time, when aspirating a red blood cell component of a liquid sample having high viscosity. When aspirating the red blood cell component of a blood sample through a nozzle tip, a piston is pulled at its maximum to produce a maximum aspirating force, and starts aspiration. When a pressure in an aspirating system becomes equal to a predetermined value α, the piston is returned to a position in which only a necessary aspiration volume of the liquid sample can be aspirated. Since the maximum aspirating force of the pump is utilized during the aspiration, the aspirating operation can be carried out more quickly.

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of Utilization

The present invention relates to a liquid aspirating method and moreparticularly to a liquid aspirating method which is used in a pipettingapparatus for pipetting a high-viscosity liquid such as a red blood cellcomponent or the like.

PRIOR ART

Various kinds of tests are conducted on a blood sample collected from ahuman body. For example, in a blood type test, as shown in FIG. 10, acollected blood sample 10 is put into a test tube 12 and is thenseparated into a blood plasma component 14 and a red blood cellcomponent 16 by centrifuging it or leaving it as it is. Practically, asmall quantity of white blood cell component 18 appears between theblood plasma component 14 and the red blood cell component 16. Since thewhite blood cell component 18 is not relevant to the followingdescription of the present invention, it is not shown in other drawings.

A blood sample pipetting method which is carried out in a conventionalpipetting apparatus generally comprises two processes, including aprocess of pipetting blood plasma and a process of pipetting red bloodcells. In the blood plasma pipetting process, the blood plasma component14 is aspirated through a nozzle tip 20, and then dispensed into aplurality of other recipient containers 22 in a predetermined volume,respectively. In the red blood cell pipetting process, the red bloodcell component 16 is aspirated through the nozzle tip 20, and thentransferred to a diluting container (not shown) to be mixed with adiluent. Thereafter, the diluted red blood cell component 16 isaspirated again through the nozzle tip 20 and then dispensed into eachof a plurality of other recipient containers 24, respectively in apredetermined volume.

Blood type testing reagents (i.e., a reagent for the blood plasmacomponent and a reagent for the red blood cell component) are introducedinto the recipient containers 22, 24, respectively.

Then, these recipient containers 22, 24 are conveyed to an agglutinationtesting apparatus, where agglutination of the samples in the containers22, 24 are measured optically or visually. On the basis of the resultsof the measurements, A type, B type, 0 type or AB type, or Rh type, orthe like is determined.

FIG. 11 shows schematically a construction of an aspirating section of aconventional pipetting apparatus. To the nozzle tip 20, a pump 104 forproducing an aspirating force and a dispensing force is connected via anair hose 102. The pump 104 includes a syringe 106 and a piston 108. Bymoving the piston 108 upwardly and downwardly, an inside volume of thesyringe 106 varies, and this inside volume variation is transmitted tothe nozzle tip 20 via the air hose 102 to generate the aspirating forceor the dispensing force. The aspirating volume (or dispensing volume) isdetermined, depending on a moving amount of the piston 108.

FIG. 12 shows a general relationship between a time elapsed afterstarting of movement of the pump 104 and a pressure in an aspiratingsystem detected by a pressure sensor 110.

As shown in FIG. 12, in case where the piston 108 has been moved by apredetermined distance within a pump moving time, characteristics of thepressure change depending on the viscosity of the blood sample to beaspirated. When a predetermined aspirating pressure is produced by thepump 104 to aspirate a predetermined volume of the blood sample, awaiting time becomes longer in accordance with increase of the viscosityof the liquid sample. As well known, the red blood cell component is ahigh-viscosity liquid (or a gel-like substance). So, when aspirating thered blood cell component through the nozzle tip 20, the aspirationvolume does not follow the moving amount of the piston 108 quickly.After a predetermined time lapses after the aspiration starts, apredetermined volume of the liquid sample is aspirated. Thepredetermined time, i.e. the waiting time becomes longer with theincrease of the liquid viscosity.

PROBLEMS TO BE SOLVED BY THE INVENTION

As aforementioned, when aspirating a predetermined volume of the liquidsample in the conventional pipetting apparatus, the moving amount of thepiston 108 is determined in accordance with the predetermined volume ofthe liquid sample. The pressure sensor 110 monitors completion of theaspiration of the predetermined volume of the liquid sample into thenozzle tip 20.

Consequently, when aspirating the red blood cell component having highviscosity, it is impossible to aspirate it quickly. As a result, it isimpossible to improve the pipetting ability per unit time of thepipetting apparatus.

For example, a liquid having a viscosity of about 100 cp requires awaiting time about ten times that required in the water having aviscosity of about 1 cp. Specifically, it takes five, to ten seconds foraspirating the liquid of about 100 cp at one time. Therefore, in anautomatic pipetting apparatus for pipetting a large volume of the liquidsample, the pipetting ability per unit time in the aforementioned caseis one-tenths of the water.

The present invention has been made in view of above problems. It istherefore an object of the present invention to provide a liquidaspirating method which enables to shorten a required aspirating time asmuch as possible, when aspirating a liquid sample, especially a bloodsample having high viscosity, in an aspirating apparatus for aspiratingthe liquid sample.

MEANS FOR SOLVING THE PROBLEMS

According to the present invention, the aforementioned object isachieved by a liquid aspirating method in an aspirating apparatusincluding a nozzle tip for aspirating a liquid sample, an aspirationpump having a piston and a syringe connected with said nozzle tip, and apressure sensor for monitoring a pressure in an aspirating system, inwhich an aspirating volume of said liquid sample into the nozzle tip isdetermined on the basis of a moving amount of said piston, wherein saidmethod comprising the steps of:

(a) setting the moving amount of said piston to such a degree that canaspirate a liquid sample more than a necessary aspirating volume intothe nozzle tip, when starting aspiration; and

(b) returning the moving amount of the piston to such a degree that canaspirate only the necessary aspirating volume into the nozzle tip, whenthe pressure in the aspirating system becomes equal to a predeterminedpressure, thereby aspirating only the necessary volume of the liquidsample into the nozzle tip.

OPERATION OF THE INVENTION

In the aforementioned features, a moving amount of the piston is firstset to a degree that can aspirate a liquid sample more than a necessaryaspiration volume. Thereafter, the moving amount of the piston isreturned to the degree that can aspirate only the necessary aspirationvolume when the pressure of the aspirating system becomes equal to apredetermined pressure. Therefore, it is possible to set an initialaspirating pressure to a high value, especially in case of aspiration ofa high-viscosity liquid. As a result, an aspiration time is shortened asa whole, and quick aspiration can be achieved. That is, since the movingamount of the piston is set to a degree that can aspirate the liquidsample more than the necessary aspiration volume, a volume more than thenecessary volume is aspirated, if the piston is kept as it is. However,in the present invention, the piston is returned just before an actualaspiration volume exceeds the necessary volume, therefore only thenecessary aspiration volume can be aspirated, finally.

This operation will now be described with reference to FIG. 13. FIG. 13shows the relationship between an elapsed time and a pressure in anaspiration system during the aspiration. According to the presentinvention, the piston is moved downwardly so as to aspirate the liquidsample more than the necessary aspiration volume during a pump movingtime. So, at a time when the pump moving time elapses, the aspirationforce becomes greater than that by a conventional method. For example, amaximum aspirating force of the pump is produced. When the pressure inthe aspirating system becomes equal to a predetermined pressure α, themoving amount of the piston is returned to the degree in which only thenecessary aspiration volume of the liquid sample can be aspirated,whereby the aspiration force is immediately reduced. Finally, only thenecessary aspiration volume of the liquid sample is aspirated into thenozzle tip.

In FIG. 13, since the moving amount of the piston is determined to be apredetermined value (maximum) for each of liquid samples havingdifferent respective viscosities, the inclination of the characteristiccurve showing a pressure during the pump moving time somewhat differsdepending on the viscosity of the liquid sample to be aspirated. In FIG.1B, t₁, t₂, t₃ designate times of termination of the aspiration for theliquid samples having different viscosities, respectively.

EMBODIMENTS

Embodiments of the present invention will now be described withreference to the accompanying drawings.

FIG. 1 shows a perspective view showing schematically a pipettingapparatus 30 in which an aspirating method according to the presentinvention is used.

In this embodiment, the apparatus 30 pipettes the blood plasma componentand the red blood cell component obtained by centrifugation to perform apreprocess for blood type test.

In the roughly central portion of FIG. 1, there is shown a nozzle 32 foraspirating a blood sample, which is held by an XYZ robot 34 so as to bemovable three-dimensionally.

FIG. 2 shows a cross sectional view of a main part of the nozzle 32. Thenozzle 32 is composed of a nozzle base 35, and a disposable tip 36(hereinafter called "tip") serving as a nozzle tip. Thus, the pipettingapparatus in the embodiment of the present invention uses a disposabletype nozzle tip. A distal end of the nozzle base 35 is forced into anupper opening of the nozzle tip 36 and is fitted therein. Thus, thenozzle tip 36 is fixed firmly to the nozzle base 35. The nozzle tip 36has at its lower end a smaller orifice 36a from which the blood sampleis aspirated and dispensed. The nozzle tip 36 may be made of a hardplastic material or the like, and the nozzle base 35 may be made of ametal.

In FIG. 1, the XYZ robot 34 is composed of an X drive portion 34x, an Ydrive portion 34y and a Z drive portion 34z. On the Z drive portion 34z,an elevator 38 equipped with the nozzle 32 is mounted so as to bevertically movable. The elevator 38 has a limit switch 40 serving as ajamming sensor or the like.

The limit switch 40 detects an external force imparted upwardly to thenozzle 32 and having a value greater than a predetermined force.

Onto the Z drive portion 34z, a diluent pipette 42 for dispensing adiluent is fixedly mounted. An air hose 44 is connected at one endthereof to the nozzle 32 and at the other end thereof to a syringe 46serving as a pump for causing aspirating and dispensing actions. Adiluent hose 48 is connected at one end thereof to the diluent pipette42 and at the other end thereof to a syringe 52 via an electromagneticvalve 50.

Between the syringe 46 and the nozzle 32, a pressure sensor 54 formeasuring an internal pressure of the air hose 44 is connected. A signalfrom the limit switch 40 is fed to the apparatus via a cable 56.

On a test tube rack 60 placed on a pipetting table 58, a plurality oftest tubes 62 each containing a blood sample which has been alreadysubjected to a centrifugation treatment are held uprightly. Each testtube 62, as shown in FIG. 10, contains the blood sample in which theblood plasma component and the red blood cell component are separated inan upper portion and a lower portion of the test tube 62, respectively.On a horizontal table 64 mounted on the pipetting table 58, a dilutiontray 68 equipped with a plurality of diluting containers 66, and amicroplate 70 are placed. On the microplate 70, there are provided aplurality of wells each serving as a recipient container for containingthe blood plasma component or the diluted red blood cell component.After all of the blood samples have been pipetted, the microplate 70 isconveyed to an apparatus for blood type test, by which an agglutinationtest, for example, is made optically. Further, the agglutination testmay be made visually.

In the apparatus of the present invention, the nozzle tip is adisposable type. A plurality of new nozzle tips are prepared on a nozzletip stand 72, and the nozzle tip already used is exchanged with a newone. There is also provided a nozzle scrap tray 74.

Therefore, in the apparatus according to the present invention, it ispossible to aspirate the blood plasma component or the red blood cellcomponent through the nozzle tip 36 of the nozzle 32 and then transferit into other recipient container. This apparatus may also be applied topurposes other than pipetting of the blood sample. Various kinds ofapplications are possible.

FIG. 3 is a block diagram of the apparatus of the embodiment accordingto the present invention. By moving a piston 76 up and down, insidevolume of the syringe 46 varies, so that an aspirating pressure or adispensing pressure is transmitted to the nozzle tip 36 of the nozzle 32via the air hose 44 to perform the aspiration or dispensation of theblood sample. The internal pressure of the air hose 44 is detected bythe pressure sensor 54, a detected signal outputted from the pressuresensor 54 is amplified by a DC amplifier 78 and is then fed to ananalog-digital converter 82 via a limiter circuit 80. The limitercircuit 80 functions as a protection circuit for suppressing anyexcessive input. The analog-digital converter 82 converts the sensorsignal into a digital signal and feeds the digital signal to a controlunit 84.

The control unit 84 includes a computer, for example, for controllingthe inside volume of the syringe 46, and the XYZ robot 34, etc. In thisembodiment, the control unit 84 also includes a viscosity measuring unit86 and a table 88. The details of the viscosity measuring unit 86 andthe table 88 will be below.

Embodiments of the pipetting method according to the present invention,which is preferably used in the above-mentioned apparatus will now bedescribed below.

FIGS. 4 and 5 show a blood plasma pipetting process. FIG. 4 shows ablood plasma component aspirating process, and FIG. 5 shows a bloodplasma component dispensing process.

In FIG. 4, at step 101, the nozzle tip 36 is lowered from the upper sideof the test tube 62 and is stopped so that the distal end of the nozzletip 36 is inserted into the blood plasma component 90 to be positionedat a predetermined distance L1 downward from a blood surface. L1 ispreferably 2 to 3 mm. If the distal end of the nozzle tip 36 is insertedtoo deeply into the blood plasma component 90, the two components onceseparated by centrifugation are likely to be mixed again with eachother.

When the nozzle tip 36 is lowered, the liquid surface is detected. Thisliquid surface detection is performed by monitoring the internalpressure of the hose 44 by the pressure sensor 54. When the internalpressure of the hose 44 is changed sharply, the control unit 84 detectsthat the distal end of the nozzle tip 36 has reached the liquid surface.

At step 102, the blood plasma component 90 is aspirated. Specifically,the piston 76 is pulled downwardly to increase the inside volume of thesyringe 46, whereby the blood plasma is aspirated into the nozzle tip36. For example, about 30 to 300 μl of the blood plasma 90 is aspirated.As described in detail below, this aspirated blood plasma componentincludes a small volume of blood plasma component to be used for aplasma coating. Preferably, the volume of blood plasma component to beaspirated should be determined by taking account of the volume of bloodplasma component that finally would attach onto an inner surface of thenozzle tip 36 and would not be dispensed from the nozzle tip 36.

At step 103, the nozzle tip 36 is raised and stopped temporarily justbefore the distal end of the nozzle tip 36 leaves from the liquidsurface of the blood plasma component 90. After a lapse of, for example,about 0.25 sec., the nozzle tip 36 is raised again at step 104. Thereason why the step 103 is needed in this process is that the bloodplasma component attaching onto an outer surface of the nozzle tip 36 isreturned into the test tube 62, as much as possible thereby improvingthe precision of the pipetting. Next to step 104, step 105 of FIG. 5 isexecuted.

In the blood plasma dispensing process shown in FIG. 5, at step 105, thenozzle tip 36 is lowered into a predetermined well 92 and is stopped sothat the distal end of the nozzle tip 36 is positioned at a distance L2off the bottom of the well 92. In this case, L2 is preferably about 2mm. If the blood plasma component is dispensed from a too high position,it would become a drop, so that it is difficult to transfer the bloodplasma component into the well 92 quickly. Further, if the distal end ofthe nozzle tip 36 comes into contact with the bottom of the well 92, itbecomes very difficult to dispense the blood plasma component.

For these reasons as stated in the above, preferable distance L2 isabout 2 mm in view of the property of the liquid to be dispensed.

At step 106, a part (predetermined volume) of the blood plasma componentexisting in the nozzle tip 36 is dispensed.

At step 107, the nozzle tip 36 is lowered until its distal end comesinto slight contact with the bottom of the well 92. The contactcondition can be monitored by the limit switch 40. At step 108, thenozzle tip 36 is raised. Namely, in step 107 and step 108, a so-calledvertical touch-off system is employed, so that the blood plasmacomponent attaching onto the inner surface of the nozzle tip 36 can bedispensed quickly.

At step 109, the nozzle tip 36 is raised and the same dispensing steps(S105-S109) are repeated with respect to other wells. Finally, apredetermined volume of blood plasma component remains in the nozzle tip36, as shown at step 109 in FIG. 5. This predetermined volume ispreferably 15 to 20 μl. The final step 109 of the blood plasmadispensing process shown in FIG. 5 corresponds to a coating preparingstep, in which a small volume of blood plasma component remains in thenozzle tip 36 for the purpose of plasma coating.

FIGS. 6 through 9 show the red blood cell pipetting process, whichgenerally comprises the following four processes including a bloodplasma coating process of FIG. 6; a red blood cell aspirating process ofFIG. 7; a red blood cell diluting process of FIG. 8; and a red bloodcell diluted solution dispensing process of FIG. 9.

Firstly, the blood plasma coating process will now be described withreference to FIG. 6. After step 109 of FIG. 5, step 200 of FIG. 6 isexecuted. Namely, by the XYZ robot 34, the nozzle tip 36 is positionedabove the test tube 62 from which the blood plasma component has beenaspirated at step 102. Specifically, the nozzle tip 36 is positioned sothat its distal end is inserted slightly (to be positioned at a distanceL3 off the blood surface) into the upper opening of the test tube 62.The above position would prevent the blood plasma coating fromscattering over other blood samples and contaminating them, thusimproving the reliability of the apparatus. L3 at step 200 is preferably5 mm.

In the method of this embodiment, pipetting operation is performedcontinuously by using the same nozzle tip 36 throughout the blood plasmapipetting process and the red blood cell pipetting process.Alternatively, when these two steps processes changeover, the nozzle tip36 may be exchanged with a new one. In such a case, it is necessary toprovide a blood plasma component coating step as a preprocessing stepbefore step 200.

At step 201, the blood plasma component used for the coating whichremains in the nozzle tip 36 is aspirated (raised) again at least tosuch an extent that the red blood cell component to be subsequentlyaspirated reaches. In more detail, the inner surface of tip 36 is coatedto such an extent that the red blood cell component diluted later, i.e.,the diluted solution of red blood cells reaches.

At step 202, the blood plasma component for the coating is dispensed(lowered), and the dispensation is stopped when the plasma componentreaches the distal end of the nozzle tip 36 as shown at step 203 of FIG.6.

In this embodiment, the coating is accomplished by moving the bloodplasma component up and down only one time as shown at step 201 and step202. Alternatively, the blood plasma component may be moved up and downtwo or more times, if necessary. However, it is confirmed that moving upand down one time is sufficient for the coating.

At step 204, the nozzle tip 36 is lowered and stopped when its distalend is inserted into the blood plasma component 90 to be positioned at adistance L4 downward from the blood surface. L4 is preferably 2 to 3 mm.At step 205, the remaining blood plasma component used for the coatingis returned into the test tube 62. Thus, in order to use a valuableblood sample without wasting it, the blood plasma component for coatingis returned into the test tube 62. Although only a small volume of bloodplasma component is used for the coating in this embodiment, a largevolume of blood plasma component may be used for the coating. If a largevolume of blood plasma component is used, it is necessary to aspirate anunnecessarily large volume of blood plasma component at step 102.Further, in step 205, there is a risk that the blood plasma component ismixed with the red blood cell component when returning such large volumeof blood plasma component into the tube. Consequently, it is preferablethat the coating should be made with a small volume of blood plasmacomponent.

After step 205, step 206 of FIG. 7 is executed. At step 206, the nozzletip 36 is further lowered, so that its distal end is inserted into thered blood cell component 94. At that time, it is preferable that thedistal end of the nozzle tip 36 is located at a position of about 75%downward from the surface of the blood plasma component, where the wholeblood sample is 100%. If the nozzle tip 36 is inserted into the bloodplasma component too deeply, a large volume of red blood cell component94 attaches onto the outer surface of the nozzle tip 36. On the otherhand, if the nozzle tip 36 is inserted into the blood plasma componenttoo shallowly, it is difficult to aspirate the red blood cell componentsurely.

At step 207, the red blood cell component 94 is aspirated. In thisembodiment, for example, 80 μl of red blood cell component 94 isaspirated.

However, the red blood cell component 94 is a high viscosity liquid or agel substance, so that considerable pressure and time are needed toaspirate such red blood cell component via the smaller orifice of thedistal end of the nozzle tip 36. In this embodiment, the following twoways are used to improve the quickness of aspiration to a maximumextent. In the first way, the inner surface of the nozzle tip 36 iscoated with the blood plasma component in order to reduce the frictionalresistance of the inner surface of the nozzle tip 36 as much aspossible, thus ensuring a smooth aspiration of the red blood cellcomponent.

In the second way, an excessively large volume of red blood cellcomponent is aspirated temporarily.

Specifically, the piston 76 of the syringe 46 is drawn to a maximumextent, and thereafter the internal pressure of the air hose 44 ismonitored by the pressure sensor 54. When the internal pressure becomesequal to a predetermined value α, the piston 76 is returned, so thatonly a desired volume of red blood cell component is finally aspiratedinto the nozzle tip 36. In more detail, since a high viscosity solutionsuch as red blood cell component cannot be aspirated so as to quicklyfollow the moving amount of the syringe 46. Therefore, the maximumaspiration force is applied to the nozzle 36, at an initial aspirationstage, and the moving amount of the syringe 46 is returned to a propervalue just before a desired volume of red blood cell component isaspirated, thereby obtaining a predetermined volume of aspirated redblood cell component of which volume is to be determined by the movingamount of the syringe 46. At step 208, when a detection value of thepressure sensor 54 becomes substantially equal to an atmosphericpressure, the termination of aspiration is confirmed. Strictly, sincethe red blood cell component is aspirated into the nozzle tip 36, theinternal pressure of the air hose 44 has a tendency to become lower thanthe atmospheric pressure. Finally, at step 208, for example, 80 μl ofthe red blood cell component is aspirated into the nozzle tip 36.

In this embodiment, the aforementioned aspirating operation iscontrolled by a control means 84 in FIG. 3. In the control means 84, amemory (not shown) for storing a predetermined pressure α shown in FIG.13 is incorporated, where the predetermined pressure α can be obtaineddepending on the characteristics of the pump by ah experimental test.Further, in the embodiment of the present invention, a timer formeasuring the waiting time after the lapse of the pump moving time isalso provided. The timer causes an alarm, when the value of the timerexceeds a predetermined limit value. For example, when the nozzle 36 isplugged, the timer gives a warning.

In the embodiment of the present invention, the aspiration control ofthe red blood cell is performed as described in the above. Theaforementioned aspiration control is also suitable for the blood plasmacomponent.

At step 209, the nozzle tip 36 is raised slowly in order to keep the twoblood components stable in a separated state and in order to avoidcausing any turbulent flow. Near the liquid surface of the blood plasmacomponent 90, the nozzle tip 36 is temporarily stopped from raising asshown in step 209, and thereafter the nozzle tip 36 is raised again atstep 210.

At step 211, for example, about 10 μl of air is aspirated to provide anair cap 99 at the distal end of the nozzle tip 36. This enables tocompletely take in the nozzle tip 36 the red blood cell componentattaching to an edge of the distal end of the nozzle tip 36, and toprevent the red blood cell component from dropping from the nozzle tip36.

After step 211, step 212 of FIG. 8 is executed. In the step 212, thenozzle tip 36 is conveyed to an upper position above the dilutingcontainer 66, at which a predetermined volume of diluent is dispensedinto the diluting container 66 through the diluent pipette 42. At step213, the nozzle tip 36 is lowered from the upper position, so that itsdistal end is positioned in the diluent 96 at a predetermined distanceL5 off the bottom of the diluting container 66. L5 is preferably 2 mm. Aphysiological salt solution can .be used for the diluent.

At step 214, the diluent 96 is aspirated into the nozzle tip 36. In theconventional method, the red blood cell component was dispensed to bemixed and diluted with the diluent. However, in this embodiment, in viewof the facts that the red blood cell component is a high viscosity anddispensation thereof is relatively difficult, the diluent which is easyto be aspirated is previously aspirated, and then the diluent is mixedwith the red blood cell component step by step.

At step 215, the mixed solution is dispensed from the nozzle tip 36 intothe diluting container 66. At that time, since the red blood cellcomponent is previously diluted by the diluent to a certain degree, themixed solution can be dispensed extremely easily, as compared with thedispensation of a pure red blood cell component. At step 216, the mixedsolution, i.e., the diluted solution of red blood cell is aspirated. Inthis embodiment, step 215 and step 216 are repeated about five times.During the successive steps from step 214, the aspiration ordispensation is initially performed slowly, depending on the viscosityof the substance to be aspirated or dispensed, and thereafterprogressively more quickly. At step 214, since the inner surface of thenozzle tip 36 has been previously coated with the blood plasmacomponent, the diluent can be aspirated into the nozzle tip 36 moresmoothly than the case in which the inner surface of the nozzle tip 36is not coated with the blood plasma component.

At step 217, the nozzle tip 36 is stopped temporarily from being raisedwhen its distal end reaches near the liquid surface, and then the nozzletip 36 is raised again.

A process of dispensing the diluted solution of the red blood cellsolution will now be described.

After step 217, step 218 of FIG. 9 is executed. The nozzle tip 36 isconveyed to a predetermined well 98 on the microplate by the XYZ robot.The nozzle tip 36 is lowered, so that its distal end is positioned inthe well 98 at a predetermined distance L6 downward from the upperopening of the diluting container 66, as shown at step 218. L6 ispreferably about 3 mm. Though there is not shown in the drawings, apredetermined volume of reagent has been previously pipetting into therespective wells 98.

At step 219, a predetermined volume of diluted solution of red bloodcell component in the nozzle tip 36 is dispensed, and then a drop of thediluted solution formed at the distal end of the nozzle tip 36 isattached onto the inner surface of the well 98 at step 220. Namely atstep 220, by using the horizontal touch-off system, the diluted solutionof red blood cell component is dispensed, without bringing the distalend of the nozzle tip 36 into direct contact with the reagent in thelower portion of the well, thereby preventing contamination from beingcaused.

At step 221, the nozzle tip 36 is raised and then moved to a next well,and thereafter the steps from step 218 to step 221 are repeatedlyexecuted.

In this embodiment, after the blood plasma pipetting process and the redblood cell pipetting process have been executed for a specific bloodsample, the nozzle tip 36 is exchanged with a new one. By using this newnozzle tip, the blood plasma pipetting process and the red blood cellpipetting process are executed in the same way for other blood samples.

The viscosity measuring unit 86 of FIG. 3 will now be describedhereinbelow. The viscosity of the red-blood cell component is valuableinformation for diagnosing an illness and is also a valuable materialfor determining an aspiration pressure to be set when a blood sample ispipetted. In the conventional apparatus, there is not provided anyviscosity measuring unit, and the viscosity of a blood sample ismeasured by a separate measuring instrument. Therefore, after havingbeen subjected to the viscosity measurement, the blood sample has beendisused. Further, the viscosity measurement takes a long time and needsa complex operation.

In the apparatus of the present invention, since the control unit 84 isequipped with the viscosity measuring unit 86, it is possible to measurethe viscosity of the blood sample while the blood sample being pipetted.

In various liquids having different viscosities, there is a closerelationship between the viscosity of each liquid and the time requiredfrom a point of time when a predetermined pressure is produced as aninitial aspiration pressure for aspirating the liquid to a point of timewhen the aspiration pressure reaches a certain pressure value. It wasconfirmed in a simulation that there is a proportional relation shiptherebetween.

In a table 88, there is stored data which represents a relationshipbetween the viscosity of the liquid to be aspirated and the timerequired from a point of time when the liquid begins to be aspiratedunder a certain initial aspiration pressure to a point of time when thepressure which returns gradually to an atmospheric pressure reaches aspecifically set pressure value.

Specifically, when aspirating the blood sample into the nozzle tip 36,the internal pressure of the air tube 44 is monitored by the pressuresensor 54, and the viscosity measuring unit 86 measures the timerequired from a point of time when the piston 76 is drawn to give theinitial aspiration pressure, to a point of time when the internalpressure of the air tube 44 reaches a predetermined value. The viscositymeasuring unit 86 also obtains a viscosity of the blood sample bycomparing the measured time with the table 88. The obtained viscosity isindicated on a display unit (not shown), and this result is utilized forcontrolling the syringe 46 by the control unit 84.

According to the viscosity measuring unit 86 described above, there areadvantages as follows. Since the viscosity can be measuredsimultaneously with the aspiration of the blood sample, the unit 86requires no additional time for measuring the viscosity, and realizes avery simple viscosity measurement. Further, it is unnecessary to preparean additional blood sample only for viscosity measurement.

ADVANTAGEOUS EFFECTS OF THE INVENTION

As aforementioned, according to the present invention, at a startingtime of the aspiration of the liquid sample, the aspirating force whichis greater than that by a conventional method can be produced. When thepressure of the aspirating system becomes equal to the predeterminedvalue, the moving amount of the piston is returned to such a degree thatonly a necessary aspiration volume of the liquid sample can beaspirated, and finally, only the necessary aspiration volume can beaspirated. Therefore, when the liquid sample having high viscosity isaspirated, it can be aspirated in a short time. For example, in thepipetting apparatus, there is advantages of improving a pipettingoperation and pipetting ability.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic view showing an embodiment of a pipettingapparatus in which an aspirating method of the present invention isused;

FIG. 2 is a cross-sectional view showing a main part of a nozzle;

FIG. 3 is a block diagram of the pipetting apparatus of FIG. 1;

FIG. 4 is an explanatory view showing steps, in which blood plasma isaspirated into the nozzle during a process of pipetting blood plasma;

FIG. 5 is an explanatory view showing steps, in which the blood plasmais dispensed from the nozzle during a process of pipetting the bloodplasma;

FIG. 6 is an explanatory view showing steps, in which the inner surfaceof the nozzle is coated with the blood plasma during a process ofpipetting red blood cells;

FIG. 7 is an explanatory view showing steps, in which red blood cellsare aspirated into the nozzle during the process of pipetting the redblood cells;

FIG. 8 is an explanatory view showing steps, in which the red bloodcells are diluted during the process of pipetting the red blood cells;

FIG. 9 is an explanatory view showing steps, in which a red blood celldiluent is dispensed from the nozzle during the process of pipetting thered blood cells; and

FIG. 10 is an explanatory view showing an operation of pipetting theblood plasma and the red blood cells as a preprocess for a blood typetest.

FIG. 11 is a schematic view showing an aspirating portion of thepipetting apparatus;

FIG. 12 is a characteristic graph showing a general relationship betweenan elapsed time and an aspirating pressure in the aspirating system whenaspirating each of liquid samples having different viscosities; and

FIG. 13 is a characteristic graph showing the relationship between theelapsed time and the aspiration pressure when the aspirating method ofthe present invention is used.

EXPLANATION OF REFERENCES NUMERALS

30 pipetting apparatus

32 nozzle

34 XYZ robot

35 nozzle base

36 disposable tip

54 pressure sensor

84 control unit

86 viscosity measuring unit

90 blood plasma component

94 red blood cell component

What is claimed is:
 1. A liquid aspirating method for use with anaspirating apparatus which includes a nozzle tip for aspirating a liquidsample, an aspirating pump having a piston and a syringe connected withsaid nozzle tip, and a pressure sensor for monitoring a pressure in anaspirating system, in which an aspirating volume of said liquid sampleinto the nozzle tip is determined on the basis of a moving amount ofsaid piston, wherein said method comprising the steps of:(a) moving saidpiston to aspirate a liquid sample more than a necessary aspiratingvolume into the nozzle tip, when starting the aspiration; and (b) movingthe piston to aspirate only the necessary aspirating volume into thenozzle tip, when the pressure in the aspirating system becomes equal toa predetermined pressure; thereby aspirating only the necessary volumeof the liquid sample into the nozzle tip.